Tallest U.S. wind tower under construction in Iowa

By early 2016, the country’s tallest onshore wind-turbine tower — and one of only a very few made from concrete rather than steel — will be operating on a wind farm in southwestern Iowa, according to an announcement today by MidAmerican Energy.

The company, which soon will have 3,300 megawatts of wind power capacity in Iowa, decided to experiment with a new technology that might allow it to access better and faster winds that blow above the heads of most wind turbines in operation.

This tower will span 377 feet from the ground to the hub, where the blades are attached to the structure. MidAmerican’s towers typically stand about 263 feet tall. If this turbine succeeds, the company likely will invest in more tall concrete towers, according to spokeswoman Ruth Comer.

“We are looking for all kinds of technologies that allow us to take advantage of wind resources,” she said. The wind generally blows faster higher up, which can make wind energy more economical than energy that’s generated at a lower altitude.

Mike Gehringer, MidAmerican’s vice president for renewable energy, added: “Advancements in turbine design and construction techniques are opening up new opportunities for development of renewable resources.”

Siemens designed and is constructing the tower as part of a 154-megawatt wind farm. The tower will be made of concrete pieces that will be cast on site, then assembled.

Concrete towers have made inroads in several other countries, most notably Spain, Brazil and Poland. There is one concrete wind-turbine tower in the U.S. Also located in Iowa, near Iowa City, it stands about 100 meters tall and is generating electricity for a nearby power company.

Steel towers pose physical and financial constraints that do not dog concrete designs, according to Sri Sritharan, the Wilson Engineering Professor at Iowa State University.

He is working on a concrete tower design with support from a $1.25 million Department of Energy grant. The only way to make a tower taller is to also make it wider at the base, Sritharan said. But highway overpasses are only so tall, and they cannot accommodate wider bases, he said.

Sritharan has devised a tower made of concrete blocks. Made in two different shapes — a panel and a column — they can be assembled in an endless variety of forms. Because they are relatively small, he said, transporting them is not a problem.

Another advantage of building out of concrete, according to Sritharan, is that concrete is much more widely available than steel, meaning parts don’t need to be shipped nearly as far.

Despite their attributes, tall towers made of concrete are yet to gain in popularity in the U.S. But company officials hope the latest project will be a catalyst for more concrete wind towers that open more low-to-medium wind resource areas to development.

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